accel/habanalabs: add debugfs interface for HLDIO testing

Add debugfs files for NVMe Direct I/O (HLDIO) functionality.
This interface allows userspace access to direct SSD ↔️

 device transfers
through debugfs nodes.

Four debugfs files are created under /sys/kernel/debug/habanalabs/hlN/:

  - dio_ssd2hl : trigger SSD-to-device transfers
  - dio_hl2ssd : trigger device-to-SSD transfers
    (placeholder, not yet implemented)
  - dio_stats  : show transfer statistics
  - dio_reset  : reset statistics counters

Usage examples:

  # Perform SSD → device transfer
  echo "fd=3 va=0x10000 off=0 len=4096" > \
    /sys/kernel/debug/habanalabs/hl0/dio_ssd2hl

  # View statistics
  cat /sys/kernel/debug/habanalabs/hl0/dio_stats

  # Reset counters
  echo 1 > /sys/kernel/debug/habanalabs/hl0/dio_reset

This interface provides access to HLDIO functionality for validation
and diagnostics.

Signed-off-by: Konstantin Sinyuk <konstantin.sinyuk@intel.com>
Reviewed-by: Farah Kassabri <farah.kassabri@intel.com>
Reviewed-by: Koby Elbaz <koby.elbaz@intel.com>
Signed-off-by: Koby Elbaz <koby.elbaz@intel.com>